1. Field of Invention
The present invention relates generally to a method and composition for patching air filter leaks, and, more particularly, to a method and patch for patching high efficiency air filter leaks without blocking significant parts of the filter and for allowing for active filtration after application of the patch to a leak or hole in the filter.
2. Description of Prior Art
High efficiency air filters, commonly called HEPA or ULPA air filters, are widely used to produce particle free air in a variety of industrial and commercial facilities. The activity and processes taking place within many of these facilities will be adversely affected by contamination from particles in the airflow. These particles can include, for example, contaminants that adversely affect drugs produced in a pharmaceutical plant, cause a defect in a semiconductor wafer, or act as an undesirable foreign body in a drug compounded in a pharmacy.
Particle contamination mainly occurs due to leaks in filters that allow unfiltered air to pass through the filter, and affect the cleanliness of the facility. For this reason, leaks in HEPA and ULPA air filters are not acceptable, and hence are conventionally repaired or patched as shown in FIG. 1 (discussed below). Leaks in filters usually occur due to pinhole size blemishes caused during filter manufacturing or during use. Guidelines for acceptable repairing practice are given in most of the prevailing national and international standards (as should be appreciated by those skilled in the art, and need not be repeated herein).
As seen in FIGS. 1a-b, HEPA and ULPA air filters 10 are constructed by pleating filter media 100 into an accordion style construction. FIG. 1a shows a schematic face view of a cross section of an air filter 10 illustrating accordion style pleated air filter media 100 common to HEPA and ULPA air filters. The pleat shape and size as well as the method of holding the filter media 100 in place vary to accommodate the end use. The media 100 used in most HEPA and ULPA filters are made from micro fiberglass with fiber diameters as small as 200 nm and lengths of a few millimeters. These fibers are held together in a thin web by a small quantity of polymeric binder. The most common polymeric binder used for such media are thermosetting or thermoplastic acrylic ester latex polymers with other additives such as water repellants that are proprietary to the manufacturer of these media. These webs are about 0.5 mm thick and are usually made on a paper machine from a slurry of fibers and to which the polymeric binder is added either in the slurry or separately.
Typical fibrous structures of such filter media 100 and its multiple fiber layers are shown in magnified (scanning electron microscope (“SEM”)) views in FIGS. 2a-b. Although each layer of the media appears to be inhomogeneous, a typical media is made up of several hundred layers of fibers. Thus, only a true blemish or pinhole will result in a leak that will require repair.
FIG. 1b is an expanded view of a portion of the air filter 10 as shown in FIG. 1a. FIG. 1b illustrates a section which contains a suspected leak that needs to be patched. As shown in FIG. 1b, current repair practice uses polymeric sealing or caulking compounds 120 to seal/patch the area around a suspected leak 110. Conventional sealing compounds 120 include silicone and silicone based caulks, poly urethane, and other similar caulking compounds. Most of the time, since leaks are repaired in the field on installed filters, a caulk like consistency is required for the sealing compound to permit repairs overhead in ceilings, for example. In cases where it is practical, such as in a factory, a nearly liquid sealant is poured into the space between the folded filter media near the location of the leak. This blocking technique, while effective in sealing the leak 110, blocks significant parts of the filter 10 thereby reducing the filter's effectiveness (dark patch 120). Further, the application of such sealing or caulking compounds 120 to seal leaks 110 in filters 10 already installed in ceilings, for example, often proves to be a cumbersome and inefficient procedure.